The present invention relates to a device for measuring the electrical potential of the inner conductor in an encased high-voltage switching mechanism which is filled with a gaseous insulator.
A device of this type is disclosed in general in the article "The ESPOM, A Capacitor--Coupled Electronic Voltage Transformer" by M. Groenenboom and H. A. J. M. Spoorenberg, which appeared in the publication Smit-Mededelingen No. 4, 1969 of the Smit Nijmegen Electrotechnische Fabriken N.V. In the operation of this disclosed device, high-voltage and low-voltage capacitors operate as a voltage divider, and the voltage which is measured at the junction of the two capacitors is supplied through a test lead to an input terminal of an amplifier. The accuracy of the voltage measurement is largely dependent upon the stability of the ratio of the capacitances of the two capacitors to each other. The current delivered through the high-voltage capacitor is compensated for by the low-voltage capacitor which is connected as a feedback element of the amplifier so that the amplifier input voltage remains approximately at zero volts. Through this arrangement, a voltage measurement is obtained which is largely independent of stray, insulation and cable capacitances. However, the ratio of the capacitances is also a function of the pressure and temperature of the gaseous insulator so that considerable deviations of the measurement value from the true value can occur under some conditions.